Patent Document 1 discloses a compressor equipped with an oil reservoir chamber. An oil separation chamber is formed in the rear housing member of the compressor so as to extend in the radial direction of the rear housing member, and the oil reservoir chamber is provided below the oil separation chamber and also at the rear end of the rear housing member so as to project outwardly. A through hole connecting the oil separation chamber with the oil reservoir chamber is formed in the rear housing member. Further, the rear housing member is provided with a discharge chamber for discharging compressed refrigerant gas including misted oil and an inflow passage for connecting the discharge chamber with the oil separation chamber. The oil separation chamber is connected to a discharge hole, and a check valve unit for preventing the refrigerant gas from reversely flowing from the oil separation chamber to the discharge chamber is provided in the discharge hole.
The check valve unit has a pipe portion projecting to the oil separation chamber, and the pipe portion and the oil separation chamber constitute oil separating means. A gas return passage, which connects an annular port in a base portion provided in the check valve unit with an oil reservoir chamber, is formed in the rear housing member. The gas return passage is smaller (about 1 mm) in diameter than the through hole and functions as a passage for returning the refrigerant gas which has entered the oil reservoir chamber to a discharge path including the annular port.
In the above-described compressor, compressed refrigerant gas in the discharge chamber flows into the oil separation chamber by way of the inflow passage. The refrigerant gas, which has entered the oil separation chamber, collides with the outer circumferential surface of the pipe portion and swirls around the outer circumferential surface, by which misted oil contained in the refrigerant gas is separated from the refrigerant gas. The thus separated oil collects at the bottom of the oil separation chamber and flows into the oil reservoir chamber from an inlet of the through hole.
Oil contained in the oil reservoir chamber is returned through the oil return passage to a crank chamber and others. Refrigerant gas, from which oil has been separated, is supplied to an external refrigerant circuit through a discharge pipe by way of a pipe portion, a check valve and others. Since the gas return passage is formed between the discharge path and the oil reservoir chamber of refrigerant gas, a flow of refrigerant gas is created due to a pressure difference ΔP between the oil separation chamber and the discharge path. Oil, which has been separated from refrigerant gas in the oil separation chamber, joins with the flow and immediately flows into the oil reservoir chamber through the through hole.
Patent Document 2 discloses a swash-plate type compressor equipped with an oil separation chamber. A projected portion is provided in an upper part of the rear cylinder block of the compressor, and a cyclone-type oil separation chamber is formed in the projected portion. Further, the compressor is provided with a connecting hole adjacent to the oil separation chamber and the connecting hole is connected to a muffler chamber formed in the rear cylinder block. A primary oil reservoir for collecting separated oil is formed below the oil separation chamber. A main oil reservoir is provided on the side of the oil separation chamber and the primary oil reservoir. An oil return hole connected to a swash plate chamber, which is a low pressure zone, is opened in a valve seat face at the bottom of the main oil reservoir. A reed valve made of a spring steel plate is provided in the opening of the oil return hole, and the reed valve is deformed depending on a pressure difference between a high pressure zone and a low pressure zone and capable of controlling the flow rate of oil flowing through the oil return hole.
In the above-described compressor, high-pressure compressed refrigerant gas flowing from the discharge chamber into the muffler chamber is introduced into an oil separation chamber via the connecting hole. The refrigerant gas introduced into the oil separation chamber swirls along the circumferential wall of the oil separation chamber, by which misted oil contained in the refrigerant gas is separated from the refrigerant gas by the actions of centrifugal force. The thus separated oil is collected in the primary oil reservoir and reserved in the main oil reservoir through the connecting hole due to a pressure difference between the high pressure zone and the low pressure zone.
The opening degree of the reed valve is controlled depending on a pressure difference between the high pressure zone and the low pressure zone. For example, when the pressure difference is small, the reed valve is opened to a great degree. Therefore, a greater amount of oil is returned from the main oil reservoir to the swash plate chamber through the oil return hole. When the pressure difference is great, the reed valve is opened to a small degree, and a small amount of oil is returned from the main oil reservoir to the swash plate chamber by way of the oil return hole.
However in the compressor disclosed in Patent Document 1, refrigerant gas is allowed to flow due to the pressure difference ΔP, by which oil separated from the oil separation chamber can be directly fed to the oil reservoir chamber. However, when machining constraints such as breakage of cutting tools are taken into account, the oil reservoir chamber must be arranged at a place proximate to the oil separation chamber due to the necessity for providing a small-diameter through hole (about 1 mm). On arrangement of the oil reservoir chamber at a place proximate to the oil separation chamber, the rear housing member is larger in dimension to result in a larger compressor.
In the compressor disclosed in Patent Document 2, a reed valve is provided, by which there is provided a structure to feed oil from the primary oil reservoir to the main oil reservoir due to a pressure difference between the oil separation chamber, which is a high pressure zone, and the swash plate chamber, which is a low pressure zone. However, it is quite difficult to control the opening degree of the reed valve depending on the pressure difference, when consideration is given to variations in the spring constant of a raw material of the reed valve and others in the manufacturing process. Therefore, there is a concern that the opening degree of the reed valve might not be appropriately controlled depending on the pressure difference. Specifically, the reed valve can be opened greatly when there is no intension to feed high-pressure refrigerant gas from the high pressure zone to the low pressure zone. In order to solve this problem, there is proposed an idea that a connecting hole is narrowed in such a manner that high-pressure refrigerant gas is not allowed to enter the swash plate chamber by way of the connecting hole connecting the primary oil reservoir with a main oil reservoir. However, due to the machining constraints, the main oil reservoir needs to be located at a place proximate to the primary oil reservoir. As a result, as in Patent Document 1, the compressor is made large in dimension.
As described above, the compressors disclosed in Patent Document 1 and Patent Document 2 have a problem that the flexibility of the design in arranging an oil separator and a reservoir of separated oil is reduced.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-218610    Patent Document 2: Japanese Laid-Open Patent Publication No. 5-240158